1. Field of the Invention
The present invention generally relates to video image processing apparatus and, more particularly, to a video image processing apparatus in which an analog video image is converted to a binary value and a computer hologram is formed satisfactorily by processing the video image with the use of a neural network circuit.
2. Description of the Prior Art
When an analog video image is converted to a binary value, the number of picture elements (i.e., pixels) which form the analog video image are increased, for example, to twice the number of pixels in the vertical and horizontal directions so that each pixel is now expressed by four small pixels. As a result, five gradations of expression are possible for each set of four small pixels, that is, the small pixels are rendered either all white, one pixel is rendered black, two pixels are rendered black, three pixels are rendered black or all pixels are rendered black. The pixels of the analog video image are compared with four threshold values and converted to respective expressions of the five gradations in response to the compared outputs.
If conversion or quantization is simply performed as described above, the gradation of video image is changed in a stepwise fashion thereby producing a so-called quasi-contour, thus resulting in a considerable degrading of the quality of the video image.
As a result, a prior art proposal removes the quasi-contour by mixing the analog video image with a desired noise component having no correlation to the analog video image. However, this method results in a lower signal-to-noise (S/N) ratio of the video image so that good image quality is not obtained.
Further, when a so-called computer hologram is formed, the computer hologram is output in binary form, although it is formed from an analog value. As a result, quantization noise occurs which causes the S/N ratio of a reproduced picture to be deteriorated considerably.